Preacher to lapse terribly (7)
I believe the answer is:
apostle
'preacher' is the definition.
(the apostles spread Jesus' message)
'to lapse terribly' is the wordplay.
'terribly' indicates an anagram.
'to'+'lapse'='tolapse'
'tolapse' anagrammed gives 'APOSTLE'.
(Other definitions for apostle that I've seen before include "John, perhaps" , "Leaps to find religious follower" , "James, perhaps" , "One of the biblical twelve (7)well don" , "Maybe Peter" .)